The Boss Monster game is specific in that it says only 2-4 players can play the game, but from reading all the rules, and the fact that there are more than 4 monsters, I don't understand why it cannot go to five or six. I imagine it might be because there might not be enough resource cards to go around. (Note: I've only played a couple of rounds of the digital product but just recently got the physical game.) However, if I put in the expansions would 5-6 players be more reasonable? Or is there some additional catches that keep it from allowing more than four players?
I was just considering this a few days ago:
No, there are simply not enough hero types to go around.
Because the game operates on 4 basic hero types, it is limited to 4 players for fairness. (ie each player can concentrate on one hero type in a 4 player game: A goes Thieves, B goes Clerics, C goes Fighters, D goes Mages).
If you add more players ( E & F ), then the players come into conflict over resource types ( E tries to go for Fighters. Suddenly, (depending on luck of the draw) either E or C is getting all the Fighter heroes and the other player gets nothing.
The problem magnifies more for each player as you add players beyond 4 in our thought experiment. Get to 8 players and 4 are unable to score any points.
Not very fun.
Edit/Update: Official Brotherwise opinion on the matter (from their website):
Boss Monster 2 is balanced and recommended for 2-4 players. However, if you also own the core set, it is possible to play with 5-6 players. Here are some unofficial guidelines for larger games:
Play using the Unlimited Lives variant described on page 17 of the rulebook. (Players are not eliminated upon reaching five Wounds. The game ends when a turn ends with no cards left in the Hero decks. The winner of the game is the player with the highest total Souls minus Wounds.)
For a 5-player game, start with all the Heroes and Epic Heroes from one set. Then add an extra 4-Health Cleric, Fighter, Mage and Thief. Add an extra 11-Health Cleric, Fighter, Mage, and Thief. For a 6-player game, also add an extra 6-Health Cleric, Fighter, Mage and Thief.
We are currently developing a set designed to facilitate larger multiplayer games. If you would like to share feedback on multiplayer over 4 players, please e-mail us at firstname.lastname@example.org!
If you have Boss Monster 2, you will have twice as many heroes available to you, so you could figure out how many extra heroes to add to the hero decks, presumably +25%. This would solve the problem of game length.
You would also want to balance which kind of treasures the heroes want, I assume something like:
- 5 Players: add the 2nd set of 3 player heroes
- 6 players: add the 2nd set of 4 player heroes
I'm not sure if the treasure types being less than the number of players will be a problem or not. Players are competing for heroes either way. Presumably the competition would be stronger, more ties, more heroes building up in town.
You would also have twice as many bosses to provide plenty of variance between what bosses are competing. I have tried mixing the old and new bosses, and they seem to be somewhat balanced; the one shot level ups are strong, and the repeating effects are mostly small and rather narrow.
Since these rules are untested, the next step would be to try them, and see what breaks, and then try to iterate and fix the problems, or give up if the problems are intractable.
There is now an official expansion that allows up to 6 players called Crash Landing. I don't own it yet so I can't tell how well it works, but it does address the concern in Mint's answer by adding a fifth treasure type.
The only problem with more players in Boss Monsters is that game length is dictated by a dwindling deck. More players means a faster dwindle. It's the same issue in Pandemic where a fifth player works in every level except that you will run out of cards even faster. The same thing happens with Dominion where the game ends faster because three piles will empty in fewer rounds than normal. With more cards Boss Monster could accomodate a fifth and sixth player. You are however adding time to the build phase and if you follow the rules literally the adventure phase too because that's more time waiting for five other players to take their turns before you go. The adventure phase is so simple that most people I've played with just do it simultaneously but the rules do say to perform them in order and there are a few rooms in which it matters.